For transmission of digital messages, signals are modulated by means of a modulator onto a carrier. A known transmission scheme uses a direct modulator in which a carrier and a signal input and a signal output are coupled as follows. The carrier input and the signal output are coupled to each other via two paths with a phase delay line disposed on one of the paths. Furthermore, on each of the two paths a nonlinear semiconductor component is disposed in such a way that the nonlinear semiconductor components, because of their polarity and the arrangement of the phase delay line, which has a nominal phase delay of 180.degree., are rendered conductive in unison, as a function of the carrier. Thus, the carrier is suppressed at the signal output. If a signal in the form of a modulation voltage is applied to the delay path, one or the other of the nonlinear semiconductor components are rendered conductive, as a function of the modulation voltage, which causes modulation of the carrier at the signal output. Such a modulator can also be used as a mixer. A particular embodiment of a modulator operating according to the above-mentioned principle and its use as a mixer is described in German patent DE-PS 29 44 642. The phase delay line of the modulator described in that patent consists of a conductive element having a length .lambda./2 of the center frequency of the carrier.